1. Field of the Invention.
The present invention relates generally to coating well proppant with a hardenable resin-fiber composite, and more particularly, to methods of continuously forming and suspending such composite coated proppant in a carrier liquid.
2. Description of the Prior Art.
Various methods have been developed for consolidating particulate solids such as sand into hard permeable packs in subterranean zones. The methods are useful in preventing loose or incompetent sand in subterranean formations from being produced from the formations along with formation fluids such as hydrocarbons and/or water. The consolidated particulate solid packs reduce or prevent the migration and production of sand with produced fluids when the consolidated solid packs are located between the producing formation and the well bore penetrating the formation.
A successful technique which has heretofore been utilized for forming a consolidated permeable particulate solid pack in a formation adjacent to a well bore comprises coating sand with a hardenable resin composition on the surface, suspending the coated sand in a viscous carrier liquid and then pumping the suspension by way of the well bore into the formation whereby the coated sand is deposited therein. The hardenable resin composition on the deposited sand is caused or permitted to harden whereby a consolidated permeable particulate solid pack is formed between the well bore and loose or incompetent sands in the formation.
Wells producing hydrocarbons are often stimulated by hydraulic fracturing treatments. In such hydraulic fracturing treatments, a viscous liquid (also referred to as a fracturing liquid or fluid) is pumped into a producing zone to be fractured at a rate and pressure such that one or more fractures are formed in the zone. Particulate solids for propping the fractures, commonly referred to in the art as "proppant," are suspended in a portion of the fracturing fluid so that the proppant is deposited in the fractures when the fracturing fluid is caused to revert to a thin fluid and return to the surface. The proppant functions to prevent the fractures from closing whereby conductive channels are formed through which produced fluids can readily flow.
In order to prevent the subsequent flow-back of proppant as well as loose or incompetent sand in the fractured zone with fluids produced therefrom, at least a portion of the proppant has heretofore been coated with a hardenable resin composition which is caused to harden and consolidate the proppant in the zone. Typically, the resin composition coated proppant is deposited in the fractures after a larger quantity of uncoated proppant material has been deposited therein. That is, the last portion of the proppant deposited in each fracture, referred to in the art as the "tail-in" portion, is coated with the hardenable resin composition. Upon the hardening of the resin composition, the tail-in portion of the proppant is consolidated into a hard permeable pack having sufficient compressive strength to prevent unconsolidated proppant and formation particulate solids from flowing out of the fractures with produced fluids.
While the hardenable resin compositions used in performing the above described procedures have successfully formed hard permeable consolidated particulate solid packs in subterranean zones, they often suffer from failures involving instability at high temperatures, a low resistance to stress cycling brought about by varying produced fluid flow rates, crushing under fracture closure stress and the like which result in proppant flowback, etc. In addition, due to the relatively high quantities of hardenable resin composition required and the high costs thereof, the particulate solids consolidation procedures utilized have involved high costs.
Recently, fibers have been mixed with proppant and the mixture has been deposited in fractures. The fibers function to inhibit the flow-back of proppant with produced fluids by filling channels or void spaces in the proppant pack with fibers thereby inhibiting the movement of proppant and formation particulate solids through the propped fracture. The proppant fiber mixture has also been consolidated by pumping a hardenable resin composition into the fractures containing a proppant and fiber mixture and causing the resin composition to harden whereby the mixture is consolidated into a hard permeable pack. The incorporation of fibrous material in the hardenable resin composition utilized to consolidate particulate solids is advantageous in that the consolidated solids have a greater thermal stability, a greater resistance to stress cycling, increased tensile, flexural and compressive strengths and decreased shrinkage. Also, the presence of the fibers reduces the quantity of resin composition required which results in a cost savings as well as increased consolidated particulate solid pack permeability.
Attempts have been made to incorporate fibers in hardenable resin compositions used to coat particulate solids utilizing continuous particulate solid suspension and coating techniques. However, the addition of fibers to a hardenable resin composition results in poor coating of proppant in a viscous carrier or fracturing liquid.
Thus, there are needs for methods of continuously forming and suspending hardenable resin composition-fibrous material composite coated particulate solids in carrier liquids for use in treating subterranean producing zones penetrated by well bores.